This invention relates generally to analog feedback circuits and more particularly to an analog feedback circuit using a four quadrant integrated circuit multiplier as the active element.
Analog feedback circuits are used to continuously produce a dc voltage analog which results in an operational null point from the amplitude and phase difference of two input signals. The amplitudes of the two in-phase signals is controlled by varying the gain of the active elements. To achieve the operational null point, the analog feedback amplifier is connected with a limiter, a phase detector and sample and hold integrator to complete the feedback loop. In the past, one type of analog feedback circuit employed varistor semiconductors for the variable resistance elements therein. Though generally satisfactory, the prior art varistor analog feedback circuits were somewhat unstable and noisy. In addition, they tended to be nonlinear in operation and to lack a large dynamic signal range. Another type of analog feedback circuit employed rayistor semiconductors as the variable resistance elements therein. Again, while generally satisfactory, the rayistor type analog feedback device was somewhat unstable and lacked adequate temperature stability. Other designs employing nonlinear components as replacements for the varistors presently used have been developed but have been discarded as not demonstrating sufficient improvement in system performance.